Polymers for delivering nitric oxide in vivo

ABSTRACT

Disclosed are novel polymers derivatized with at least one —NO x  group per 1200 atomic mass unit of the polymer. X is one or two. In one embodiment, the polymer is an S-nitrosylated polymer and is prepared by reacting a polythiolated polymer with a nitrosylating agent under conditions suitable for nitrosylating free thiol groups. The polymers of the present invention can be used to coat medical devices to deliver nitric oxide in vivo to treatment sites.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/164,366 filed Jun. 5, 2002, now U.S. Pat. No. 6,673,891; which is acontinuation of U.S. application Ser. No. 09/752,223 filed Dec. 29,2000, now U.S. Pat. No. 6,403,759; which is a continuation of U.S.application Ser. No. 09/103,225 filed Jun. 23, 1998, now U.S. Pat. No.6,232,434; which is a continuation in part of U.S. application Ser. No.08/691,862 filed Aug. 2, 1996, now U.S. Pat. No. 5,770,645.

BACKGROUND OF THE INVENTION

Many modern medical procedures require that synthetic medical devicesremain in an individual undergoing treatment. For example, coronary andperipheral procedures involve the insertion of diagnostic catheters,guide wires, guide catheters, PTCA balloon catheters (for percutaneoustransluminal coronary angioplasty) and stents in blood vessels.In-dwelling sheaths (venous and arterial), intraaortic balloon pumpcatheters, tubes in heart lung machines, GORE-TEX surgical prostheticconduits and in-dwelling urethral catheters are other examples. Thereare, however, complications which can arise from these medicalprocedures. For example, the insertion of synthetic materials into lumencan cause scaring and restenosis, which can result in occlusion orblockage of the lumen. Synthetic materials in the blood vessels can alsocause platelet aggregation, resulting in some instances, in potentiallylife-threatening thrombus formation.

Nitric oxide (referred to herein as “NO”) inhibits the aggregation ofplatelets. NO also reduces smooth muscle proliferation, which is knownto reduce restenosis. Consequently, NO can be used to prevent and/ortreat the complications such as restenosis and thrombus formation whendelivered to treatment sites inside an individual that have come incontact with synthetic medical devices. In addition, NO isanti-inflammatory, which would be of value for in-dwelling urethral orTPN catheters.

There are, however, many shortcomings associated with present methods ofdelivering NO to treatment sites. NO itself is too reactive to be usedwithout some means of stabilizing the molecule until it reaches thetreatment site. NO can be delivered to treatment sites in an individualby means of polymers and small molecules which release NO. However,these polymers and small molecules typically release NO rapidly. As aresult, they have short shelf lives and rapidly lose their ability todeliver NO under physiological conditions. For example, the lifetime ofS-nitroso-D,L-penicillamine and S-nitrosocysteine in physiologicalsolution is no more than about an hour. As a result of the rapid rate ofNO release by these compositions, it is difficult to deliver sufficientquantities of NO to a treatment site for extended periods of time or tocontrol the amount of NO delivered.

Polymers containing groups capable of delivering NO, for examplepolymers containing diazeniumdiolate groups (NONOate groups), have beenused to coat medical devices. However, decomposition products ofNONOates under oxygenated conditions can include nitrosamines (Ragsdaleet al., Inorg. Chem. 4:420 (1965), some of which may be carcinogenic. Inaddition, NONOates generally release NO, which is rapidly consumed byhemoglobin and can be toxic in individuals with arteriosclerosis.Further, the elasticity of known NO-delivering polymers is generallyinadequate, making it difficult to coat medical devices with the polymerand deliver NO with the coated device under physiological conditions.Protein based polymers have a high solubility in blood, which results inshort lifetimes. Finally, many NO-delivering polymers cannot besterilized without loss of NO from the polymer and amounts of NOdelivered are limiting.

There is, therefore, a need for new compositions capable of deliveringNO to treatment sites in a manner which overcomes the aforementionedshortcomings.

SUMMARY OF THE INVENTION

The present invention relates to novel polymers derivatized with NO_(X),wherein X is one or two. It has now been found that medical devicescoated with the novel polymers of the present invention are effective inreducing platelet deposition and restenosis when implanted into animalmodels. Specifically, stents coated with an S-nitrosylatedβ-cyclodextrin or an S-nitrosylated β-cyclodextrin complexed withS-nitroso-N-acetyl-D,L-penicillamine or S-nitroso-penicillamine resultedin decreased platelet deposition when inserted into the coronary orcortoid arteries of dogs compared with stents which lacked the polymercoating (Example 12). It has also been found that S-nitrosylatedβ-cyclodextrin and S-nitrosylated β-cyclodextrin complexed withS-nitroso-N-acetyl-D,L-penicillamine cause vasodilation in bioassays(Examples 8 and 10). Furthermore, compositions comprising S-nitrosylatedcyclodextrins complexed with S-nitrosothiols have been found to deliverNO-related activity for extended periods of time and to exhibitincreased shelf stability compared with compounds presently used todeliver NO in vivo. Specifically, S-nitrosylated β-cyclodextrincomplexed with S-nitroso-N-acetyl-D,L-penicillamine can be stored for atleast three weeks without losing NO and to deliver NO in physiologicalsolutions for periods of time greater than 24 hours (Example 10).Lifetimes of many months have been observed (Examples 9 and 10).

The present invention includes novel nitrated or nitrosylated polymers.Thus, the novel polymers are derivatized with NO_(X). The polymer has atleast one NO_(X) group per 1200 atomic mass units (amu) of the polymer,preferably per 600 amu of the polymer, and even more preferably per 70amu of the polymer. In a preferred embodiment, the polymer has pendant—S—NO and/or pendant —O—NO groups, i.e. the polymer is S-nitrosylatedand/or O-nitrosylated. In another embodiment, the polymer is prepared byreacting a polythiolated polysaccharide with a nitrosylating agent or anitrating agent under conditions suitable for nitrosylating or nitratingfree thiol groups.

Another embodiment of the present invention is a method of preparing apolymer having NO_(X) groups. The method comprises reacting a polymerhaving a multiplicity of pendant nucleophilic groups with anitrosylating agent or a nitrating agent under conditions suitable fornitrosylating or nitrating free nucleophilic groups. In a preferredembodiment, the polymer is a polythiolated polymer.

Another embodiment of the present invention is a method of deliveringnitric oxide to a treatment site in an individual or animal. The methodcomprises providing a medical device coated with a polymer derivatizedwith NO_(X), as described above. Preferably, the polymer is anS-nitrosylated polymer. The medical device is then implanted into theindividual or animal at the treatment site. For delivering nitric oxideto a bodily fluid, for example blood, the bodily fluid is contacted withthe coated medical device.

Yet another embodiment of the present invention is a method of preparinga device for delivering nitric oxide to a treatment site in anindividual or animal. The method comprises coating a medical devicesuitable for contacting the treatment site in the individual or animalwith a polymer derivatized with NO_(X), as described above. Preferably,the polymer is an S-nitrosylated polymer.

Another embodiment of the present invention is a medical device fordelivering nitric oxide to a treatment site in an individual or animal.The device comprises a medical device suitable for implantation at thetreatment site in the individual or animal and which is coated with apolymer derivatized with NO_(X), as described above. Preferably, thepolymer is an S-nitrosylated polymer.

Another embodiment of the present invention is a method for replacing aloss of NO groups from an S-nitrosylated polymer. The method comprisescontacting the S-nitrosylated polymer with an effective amount of agaseous nitrosylating agent such as nitrosyl chloride (NOCl) underconditions suitable for nitrosylating free thiols.

S-nitrosylated cyclodextrins of the present invention undergoheterolytic cleavage of the —S—NO group, and consequently do notprinciply release NO. These polymers have a high NO capacity andincorporation of nitrosylating agents such asS-nitroso-N-acetyl-D,L-penicillamine into the polymer matrix increasesthe stability of S-nitrosylated cyclodextrins to weeks or more. Theincorporation of nitrosylating agents also increases their capacity todeliver NO by about two fold over native cyclodextrin and by about twohundred fold over protein based polymers. The combination of increasedstability and capacity to deliver NO results in a high NO potency, acontrolled delivery of NO and extended treatment and storage lives forthe polymer. A further advantage of these polymers is that they lack thebrittleness of other NO-delivering compositions and have sufficientelasticity to coat and adhere under physiological conditions to medicaldevices such as stents.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 is a graph illustrating the number of platelets deposited persquare centimeter on stents coated with S-nitrosylated β-cyclodextrinand on uncoated control stents which had been implanted in the arteriesof dogs.

FIG. 2 is a graph illustrating the number of —S—NO groups percyclodextrin on the product resulting from the reaction ofper-6-thio-β-cyclodextrin with one (1×), two (2×), three (3×), six (6×)and ten (10×) equivalents of acidic nitrite.

FIG. 3 is the visible/ultraviolet spectrum of a reaction mixturecomprising β-cyclodextrin and a 50 fold excess of acidic nitrite, takenat intervals of (1) 5 minutes, (2) fifteen minutes, (3) thirty minutes,(4) forty-five minutes, (5) sixty minutes, (6) seventy five minutes and(7) ninety minutes.

DETAILED DESCRIPTION OF THE INVENTION

As used herein “polymer” has the meaning commonly afforded the term.Example are homopolymers, co-polymers (including block copolymers andgraft copolymers), dendritic polymers, crosslinked polymers and thelike. Suitable polymers include synthetic and natural polymers (e.g.polysaccharides, peptides) as well as polymers prepared by condensation,addition and ring opening polymerizations. Also included are rubbers,fibers and plastics. Polymers can be hydrophilic, amphiphilic orhydrophobic. In one aspect, the polymers of the present invention arenon-peptide polymers.

Preferred polymers are those which are water insoluble an hydrophilic,i.e. can form hydrogels. A hydrogel is a composition which can absorblarge quantities of water. Polymers which can form hydrogels aregenerally more biocompatible than other polymers and can be used indevices which are inserted into, for example, vascular systems.Platelets and proteins normally deposit immediately upon insertion ofpolymer into a vascular site and initiate a cascade of events leading torestenosis or injury. This process is slowed or eliminated with polymersthat form hydrogels, resulting in reduced risk of protein deposition andplatelet activation. Polymers which form hydrogels are typicallycrosslinked hydrophilic polymers. Further descriptions and examples ofhydrogels are provided in Hydrogels and Biodegradable Polymers forBioapplications, editors Attenbrite, Huang and Park, ACS SymposiumSeries, No. 627 (1996), U.S. Pat. Nos. 5,476,654, 5,498,613 and5,487,898, the teachings of which are incorporated herein by reference.Examples of hydrogels include polyethylene hydroxides, polysaccharidesand crosslinked polysaccharides.

NO_(X) is connected to the polymers of the present invention by a singlecovalent bond between the nitrogen atom of NO_(X) and a linking group M,which is pendant, or covalently bonded to the polymer. Thus, thepolymers of the present invention have pendant —M—NO_(X) groups.Examples of —M—NO_(X) groups include —S—NO_(X), —O—NO_(X), —NR—NO_(X),—CH₂—NO_(X), —NOH—NO_(X), —CO—NR—NO_(X), —NH—C(NH₂)═N—NO_(X),═N—NR—NO_(X), ═N—NO_(X), and >N—NO_(X). Also included are aliphatic andaromatic C-nitro and C-nitroso compounds. R is —H, alkyl or substitutedalkyl. Alkyl groups can be straight chained or branched and have fromabout one to about ten carbon atoms. Suitable substituents include —CN,halogen, phenyl and alkyl. The rate of NO delivery can be variedaccording to the stability of the pendant —M—NO_(X) group, with the lessstable groups having a faster rate of NO delivery than more stablegroups. —S—NO_(X) groups are generally the least stable, while —C—NO_(X)groups are generally the most stable. —O—NO_(X) are generally morestable than —S—NO_(X) groups, while —N—NO_(X) groups are generally ofintermediate stability.

In a preferred embodiment, the polymers of the present invention havependant —S—NO_(X) groups, more preferably —S—NO groups. A polymer with—S—NO groups is referred to as an S-nitrosylated polymer. An “—S—NOgroup” is also referred to as a sulfonyl nitrite, a thionitrous acidester, an S-nitrosothiol or a thionitrite. In one aspect, theS-nitrosylated polymer also has pendant —O—NO_(X) groups, preferably—O—NO groups. An “—O—NO” group is referred to as a nitrite. TheS-nitrosylated polymers of the present invention have at least one NOgroup per 1200 atomic mass unit of the polymer. For example, anS-nitrosylated polymer with a molecular weight of about 600,000 atomicmass units (amu) including the —S—NO groups would have about 500 NOgroups covalently bonded to the polymer. Preferably, the S-nitrosylatedpolymers of the present invention have at least one NO group per 600 amuof the polymer (See Example 13), and, even more preferably, at least oneNO group per 70 amu of the polymer (See Example 14).

A polymer with pendant—S—NO₂ groups is referred to as an S-nitratedpolymer. An “—S—NO₂ group” is also referred to as a sulfonyl nitrate, anS-nitrothiol or a thionitrate. —S—NO₂ groups decompose in vivo,resulting in the delivery of NO. In one aspect, an S-nitrated polymeralso has pendant —O—NO_(X) groups. The S-nitrated polymers of thepresent invention have at least one NO₂ group per 1200 atomic mass unitof the polymer. Preferably, the S-nitrated polymers of the presentinvention have as least one NO₂ group per 600 amu of the polymer, and,even more preferably, at least one NO₂ group per 70 amu of the polymer.

The polymers of the present invention can be prepared from polymershaving a multiplicity of nucleophilic groups. Suitable nucleophilicgroups include amines, thiols, hydroxyls, hydroxylamines, hydrazines,amides, guanadines, imines, aromatic rings and nucleophilic carbonatoms. To prepare a nitrosylated polymer, a polymer with a multiplicityof pendant nucleophilic groups is reacted with a nitrosylating agentunder conditions suitable for nitrosylating the nucleophilic groups. Toprepare a nitrated polymer, a polymer with a multiplicity of pendantnucleophilic groups is reacted with a nitrating agent under conditionssuitable for nitrating the nucleophilic groups. The preparation ofnitrated and nitrosylated polymers will now be described with respect toS-nitrosylated and S-nitrated polymers. It should be understood that theprocedures described herein for the preparation S-nitrosylated andS-nitrated polymers can be used for the nitration or nitrosylation ofpolymers with pendant nucleophilic groups other than thiols, asdescribed above. Although some variation in conditions may be required,such modification can be determined by one of ordinary skill in the artwith no more than routine experimentation.

S-nitrosylated polymers and S-nitrated polymers can be prepared frompolymers having a multiplicity of pendant thiol groups, referred toherein as “polythiolated polymers”. To prepare an S-nitrosylatedpolymer, a polythiolated polymer is reacted with a nitrosylating agentunder conditions suitable for nitrosylating free thiol groups. Toprepare an S-nitrated polymer, a polythiolated polymer is reacted with anitrating agent under conditions suitable for nitrating free thiolgroups. Suitable nitrosylating agents and nitrating agents are disclosedin Feelisch and Stamler, “Donors of Nitrogen Oxides”, Methods in NitricOxide Research edited by Feelisch and Stamler, (John Wiley & Sons)(1996), the teachings of which are hereby incorporated into thisapplication. Suitable nitrosylating agents include acidic nitrite,nitrosyl chloride, compounds comprising an S-nitroso group(S-nitroso-N-acetyl-D,L-penicillamine (SNAP), S-nitrosoglutathione(SNOG), N-acetyl-S-nitrosopenicillaminyl-S-nitrosopenicillamine,S-nitrosocysteine, S-nitrosothioglycerol, S-nitrosodithiothreitol andS-nitrosomercaptoethanol), an organic nitrite (e.g. ethyl nitrite,isobutyl nitrite, and amyl nitrite) peroxynitrites, nitrosonium salts(e.g. nitrosyl hydrogen sulfate), oxadiazoles (e.g.4-phenyl-3-furoxancarbonitrile) and the like. Suitable nitrating agentsinclude organic nitrates (e.g. nitroglycerin, isosorbide dinitrate,isosorbide 5-mononitrate, isobutyl nitrate and isopentyl nitrate),nitronium salts (e.g. nitronium tetrafluoroborate), and the like.

Nitrosylation with acidic nitrite can be, for example, carried out in anaqueous solution with a nitrite salt, e.g. NaNO₂, KNO₂, LiNO₂ and thelike, in the presence of an acid, e.g. HCl, acetic acid, H₃PO₄ and thelike, at a temperature from about −20° C. to about 50° C., preferably atambient temperature. Generally, from about 0.8 to about 2.0, preferablyabout 0.9 to about 1.1 equivalents of nitrosylating agent are used perthiol being nitrosylated. Sufficient acid is added to convert all of thenitrite salt to nitrous acid. Specific conditions for nitrosylating apolythiolated cyclodextrin with acidic nitrite are provided in Example3.

Nitrosylation with NOCl can be carried out, for example, in an aproticpolar solvent such as dimethylformamide or dimethylsulfoxide at atemperature from about −20° C. to about 50° C., preferably at ambienttemperature. NOCl is bubbled through the solution to nitrosylate thefree thiol groups. Specific conditions for nitrosylating a polythiolatedcyclodextrin with NOCl are provided in Example 4.

The quantity of —S—NO groups present in the composition can bedetermined by the method of Saville disclosed in “Preparation andDetection of S-Nitrosothiols,” Methods in Nitric Oxide Research, editedby Feelisch and Stamler, (John Wiley & Sons) pages 521-541, (1996). Tocalculate the amount of NO per molecular weight of polymer, the polymerconcentration, e.g. carbohydrate concentration, is also determined.Carbohydrate concentration can be determined by the method disclosed inDubois et al., Anal. Chem. 28:350 (1956).

Polythiolated polymers can be formed from polymers having a multiplicityof pendant nucleophilic groups, such as alcohols or amines. The pendantnucleophilic groups can be converted to pendant thiol groups by methodsknown in the art and disclosed in Gaddell and Defaye, Angew. Chem. Int.Ed. Engl. 30:78 (1991) and Rojas et al., J. Am. Chem. Soc. 117:336(1995), the teachings of which are hereby incorporated into thisapplication by reference.

In an especially preferred embodiment, the S-nitrosylated polymer is anS-nitrosylated polysaccharide. Examples of suitable S-nitrosylatedpolysaccharides include S-nitrosylated alginic acid, κ-carrageenan,starch, cellulose, fucoidin, cyclodextrins such as α-cyclodextrin,β-cyclodextrin and γ-cyclodextrin. Other suitable examples are disclosedin Bioactive Carbohydrates, Kennedy and White eds., (John Wiley Sons),Chapter 8, pages 142-182, (1983) the teachings of which are incorporatedherein by reference. Polysaccharides have pendant primary and secondaryalcohol groups. Consequently, S-nitrosylated polysaccharides can beprepared from polythiolated polysaccharides by the methods describedhereinabove. Preferred polysaccharides include cyclodextrins, forexample α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin. Thepolysaccharide is first converted to a polythiolated polysaccharide, forexample, by the methods disclosed in Gaddell and Defaye and Rojas et al.In these methods primary alcohols are thiolated preferentially oversecondary alcohols. Preferably, a sufficient excess of thiolatingreagent is used to form perthiolated polysaccharides. Polysaccharidesare “perthiolated” when all of primary alcohols have been converted tothiol groups. Specific conditions for perthiolating β-cyclodextrin aregiven in Examples 1 and 2. Polythiolated and perthiolatedpolysaccharides can be nitrosylated in the presence of a suitablenitrosylating agents such as acidic nitrite (Example 3) or nitrosylchloride (Example 4), as described above.

In one aspect, an excess of acidic nitrite is used with respect to freethiol groups when preparing an S-nitrosylated polysaccharide, forexample an S-nitrosylated cyclodextrin. An excess of acidic nitriteresults in a polysaccharide with pendant —S—NO and —O—NO groups. Theextent of O-nitrosylation is determined by how much of an excess ofacidic nitrite is used. For example, nitrosylation ofper-6-thio-β-cyclodextrin with a 50 fold excess of acidic nitriteresults in a product comprising about ten moles of NO for eachcyclodextrin (Example 14), or about 1 mole of NO per 140 amu.Nitrosylation of per-6-thio-β-cyclodextrin with a 100 fold excess ofacidic nitrite results in a product comprising about 21 moles of NO foreach cyclodextrin (Example 14), or about 1 mole of NO per 70 amu.Specific conditions for the preparation of β-cyclodextrin with pendant—O—NO and —S—NO groups are described in Example 14.

In another aspect, a polythiolated polysaccharide can be prepared byreacting the alcohol groups, preferably the primary alcohol groups, onthe polysaccharide with a reagent which adds a moiety containing a freethiol or protected thiol to the alcohol. In one example thepolysaccharide is reacted with a bis isocyanatoalkyldisulfide followedby reduction to functionalize the alcohol as shown in Structural Formula(I):

Conditions for carrying out this reaction are found in Cellulose and itsDerivatives, Fukamota, Yamada and Tonami, eds. (John Wiley & Sons),Chapter 40, (1985) the teachings of which are incorporated herein byreference. One example of a polythiolated polysaccharide which can beobtained by this route is shown in Structural Formula (II):

It is to be understood that agents capable of nitrosylating a freethiol, in some instances, also oxidize free thiols to form disulfidebonds. Thus, treating a polythiolated polymer (e.g. polythiolatedpolysaccharides such as polythiolated cyclodextrins) with anitrosylating agent, e.g. acidified nitrite, nitrosyl chloride,S-nitrosothiols can, in some instances, result in the formation of acrosslinked S-nitrosylated polymer matrix. A “polymer matrix” is amolecule comprising a multiplicity of individual polymers connected or“crosslinked” by intermolecular bonds. Thus, in some instances thenitrosylating agent nitrosylates some of the thiols and, in addition,crosslinks the individual polymers by causing the formation ofintermolecular disulfide bonds. Such polymer matrices are encompassed bythe term “S-nitrosylated polymer” and are included within the scope ofthe present invention. When an excess of the nitrosylating agent is usedand when the nitrosylating agent is of a sufficient size, it can beincorporated, or “entwined,” within the polymeric matrix by theintermolecular disulfide bonds which crosslink the individual polymermolecules, thereby forming a complex between the polymer and thenitrosylating agent.

S-nitrosylated polysaccharides, in particular S-nitrosylated cyclizedpolysaccharides such as S-nitrosylated cyclodextrins, can form a complexwith a suitable nitrosylating agent when more than one equivalent ofnitrosylating agent with respect to free thiols in the polythiolatedpolysaccharide is used during the nitrosylation reaction, as describedabove. Generally, between about 1.1 to about 5.0 equivalents ofnitrosylating agent are used to form a complex, preferably between about1.1 to about 2.0 equivalents.

Nitrosylating agents which can complex with an S-nitrosylated cyclicpolysaccharide include those with the size and hydrophobicity necessaryto form an inclusion complex with the cyclic polysaccharide. An“inclusion complex” is a complex between a cyclic polysaccharide such asa cyclodextrin and a small molecule such that the small molecule issituated within the cavity of the cyclic polysaccharide. The sizes ofthe cavities of cyclic polysaccharides such as cyclodextrins, andmethods of choosing appropriate molecules for the preparation ofinclusion complexes are well known in the art and can be found, forexample, in Szejtli Cyclodextrins In Pharmaceutical, Kluwer AcademicPublishers, pages 186-307, (1988) the teachings of which areincorporated herein by reference.

Nitrosylating agents which can complex with an S-nitrosylated cyclicpolysaccharide also include nitrosylating agents with a sufficient sizesuch that the nitrosylating agent can become incorporated into thestructure of the polymer matrix of an S-nitrosylated polysaccharide. Asdiscussed earlier, in certain instances nitrosylation of polythiolatedpolymers can also result in the crosslinking of individual polymermolecules by the formation of intermolecular disulfide bonds to give apolymer matrix. Suitable nitrosylating agents are those of anappropriated size such that the nitrosylating agent can be incorporatedinto this matrix. It is to be understood that the size requirements aredetermined by the structure of each individual polythiolated polymer,and that suitable nitrosylating agents can be routinely determined bythe skilled artisan according to the particular S-nitrosylated polymerbeing prepared.

Nitrosylating agents which can form a complex with S-nitrosylatedcyclodextrins include compounds with an S-nitroso group(S-nitroso-N-acetyl-D,L-penicillamine (SNAP), S-nitrosoglutathione(SNOG), N-acetyl-S-nitrosopenicillaminyl-S-nitrosopenicillamine,S-nitrosocysteine, S-nitrosothioglycerol, S-nitrosodithiothreitol, andS-nitrosomercaptoethanol), an organic nitrite (e.g. ethyl nitrite,isobutyl nitrite, and amyl nitrite), oxadiazoles (e.g.4-phenyl-3-furoxancarbonitrile), peroxynitrites, nitrosonium salts andnitroprusside and other metal nitrosyl complexes (See Feelisch andStamler, “Donors of Nitrogen Oxides,” Methods in Nitric Oxide Researchedited by Feelisch and Stamler, (John Wiley & Sons) (1996). As discussedin greater detail below, NO delivery times and delivery capacity ofS-nitrosylated cyclodextrins are increased by the incorporation ofnitrosylating agents. The extent and degree to which delivery times andcapacity are increased is dependent on the nitrosylating agent.

Specific conditions for forming a complex between an S-nitrosylatedcyclodextrin and a nitrosylating agent are provided in Examples 5 and 6.Conditions described in these examples result in nitrosylation of atleast some of the free thiols in the polysaccharide. Because an excessof nitrosylating agent is used with respect to the quantity of freethiols in the polysaccharide is used, the resulting composition containsunreacted nitrosylating agent. Evidence that the S-nitrosylatedpolysaccharide forms a complex with the nitrosylating agent comes fromthe discovery, reported herein, that the rate of NO release from thereaction product of per-(6-deoxy-6--thio)β-thiocyclodextrin andS-nitroso-N-acetylpenicillamine is extended compared withS-nitroso-N-acetylpenicillamine alone (Example 10).

Although Applicants do not wish to be bound by any particular mechanism,it is believed that incorporation of a nitrosylating agent into theS-nitrosylated cyclic polysaccharide allows both the polysaccharide andthe nitrosylating agent to deliver NO at a treatment site. It is alsobelieved that the interaction between the cyclic polysaccharide and thenitrosylating agent results in stabilization of the —S—NO functionalgroup in the nitrosylating agent. It is further believed that thepresence of a nitrosylating agent in the composition serves to feed,i.e. replenish, the nitrosyl groups in the S-nitrosylatedpolysaccharide, thereby serving to extend the lifetime during which thepolymer can serve as an NO donor.

The degree to which the lifetime of an S-nitrosylated cyclicpolysaccharide can be extended is determined by the stability of theS-nitrosyl group when the nitrosylating agent is a thionitrite. Thestability of —S—NO groups is dependent on a number of factors; theability of —S—NO groups to chelate metals facilitates homolyticbreakdown; tertiary —S—NO groups are more stable than secondary —S—NOgroups which are more stable than primary groups; —S—NO groups which fitinto the hydrophobic pocket of cyclodextrins are more stable than thosewhich do not; the proximity of amines to the —S—NO group decreasesstability; and modification at the position β to the —S—NO groupregulates stability.

It is to be understood that a complex can be formed between anS-nitrosylated polymer or an S-nitrated polymer and a nitrating agenthaving a suitable size and hydrophobicity, as described above forS-nitrosylated polymers and nitrosylating agents. Crosslinked S-nitratedcyclodextrins and complexes between an S-nitrated polymer and anitrating agent are encompassed within the term “S-nitratedcyclodextrin”. Suitable nitrating agents include organic nitrates suchas nitroglycerin, isosorbide dinitrate, isosorbide 5-mononitrate,isobutyl nitrate and isopentyl nitrate and nitronium salts. As withnitrosylating agents, the rate of NO release is dependent on whichnitrating agents is incorporated into the polymer.

In one embodiment, the present invention is a composition comprising apolymer derivatized with NO_(x) and additionally comprising otheringredients which endow the polymer with desirable characteristics. Forexample, plasticizers and elastomers can be added to the composition toprovide the polymer with greater elasticity. Generally, suitableplasticizers and elastomers are compounds which are: 1) biocompatible,i.e. which cause minimal adverse reactions such as platelet and proteindeposition in an individual to which it is administered and 2) which aresoluble in the polymer capable of delivering NO and which can, in turn,solubilize said polymer. Examples of suitable plasticizers includepolyalkylene glycols such as polyethylene glycols. Preferredplasticizers are those which can also deliver NO, for examplenitrosothioglycerol.

Another embodiment of the present invention is a method of delivering NOto a treatment site in an individual or animal using the novel polymersand compositions of the present inventions to deliver NO. A “treatmentsite” includes a site in the body of an individual or animal in which adesirable therapeutic effect can be achieved by contacting the site withNO. An “individual” refers to a human and an animal includes veterinaryanimals such as dogs, cats and the like and farm animals such as horses,cows, pigs and the like.

Treatment sites are found, for example, at sites within the body whichdevelop restenosis, injury or thrombosis as a result of trauma caused bycontacting the site with a synthetic material or a medical device. Forexample, restenosis can develop in blood vessels which have undergonecoronary procedures or peripheral procedures with PTCA balloon catheters(e.g. percutaneous transluminal angioplasty). Restenosis is thedevelopment of scar tissue from about three to six months after theprocedure and results in narrowing of the blood vessel. NO reducesrestenosis by inhibiting platelet deposition and smooth muscleproliferation. NO also inhibits thrombosis by inhibiting platelets andcan limit injury by serving as an anti-inflammatory agent.

A treatment site often develops at vascular sites which are in contactwith a synthetic material or a medical device. For example, stents areoften inserted into blood vessels to prevent restenosis and re-narrowingof a blood vessel after a procedure such as angioplasty. Plateletaggregation resulting in thrombus formation is a complication which mayresult from the insertion of stents. NO is an antiplatelet agent and canconsequently be used to lessen the risk of thrombus formation associatedwith the use of these medical devices. Other examples of medical deviceswhich contact vascular sites and thereby increase the risk of thrombusformation include sheaths for veins and arteries and GORE-TEX surgicalprosthetic.

Treatment sites can also develop at non-vascular sites, for example atsites where a useful therapeutic effect can be achieved by reducing aninflammatory response. Examples include the airway, the gastrointestinaltract, bladder, uterine and corpus cavernosum. Thus, the compositions,methods and devices of the present invention can be used to treatrespiratory disorders, gastrointestinal disorders, urologicaldysfunction, impotence, uterine dysfunction and premature labor. NOdelivery at a treatment site can also result in smooth muscle relaxationto facilitate insertion of a medical device, for example in proceduressuch as bronchoscopy, endoscopy, laparoscopy and cystoscopy. Delivery ofNO can also be used to prevent cerebral vasospasms post hemorrhage andto treat bladder irritability, urethral strictures and biliary spasms.

Treatment sites can also develop external to the body in medical devicesused to treat bodily fluids temporarily removed from body for treatment,for example blood. Examples include conduit tubes within heart lungmachines and tubes of a dialysis apparatus.

The method of delivering NO to a treatment site in an individual oranimal comprises implanting a medical device coated with a polymer ofthe present invention at the treatment site. NO can be delivered tobodily fluids, for example blood, by contacting the bodily fluid with amedical device coated with a polymer of the present invention. Apreferred polymer is an S-nitrosylated polymer, as defined above.Examples of treatment sites in an individual or animal, medical devicessuitable for implementation at the treatment sites and medical devicessuitable for contacting bodily fluids such as blood are described in theparagraphs hereinabove.

“Implanting a medical device at a treatment site” refers to bringing themedical device into actual physical contact with the treatment site or,in the alternative, bringing the medical device into close enoughproximity to the treatment site so that NO released from the medicaldevice comes into physical contact with the treatment site. A bodilyfluid is contacted with a medical device coated with a polymer of thepresent invention when, for example, the bodily fluid is temporarilyremoved from the body for treatment by the medical device, and thepolymer coating is an interface between the bodily fluid and the medicaldevice. Examples include the removal of blood for dialysis or by heartlung machines.

In one embodiment of the present invention, a medical device, forexample a stent, is coated with a polymer of the present invention. Inone example, the device is coated with an S-nitrosylated polysaccharide,preferably a cyclic S-nitrosylated or S-nitrated polysaccharide, andeven more preferably an S-nitrosylated or an S-nitrated cyclodextrin. Amixture is formed by combining a solution comprising a polythiolatedpolysaccharide with a medical device insoluble in the solution. Themixture is then combined with a nitrosylating agent (or nitrosatingagent) under conditions suitable for nitrosylating (or nitrating) freethiol groups, resulting in formation of an S-nitrosylatedpolysaccharide. In an aqueous solution, the S-nitrosylatedpolysaccharide precipitates from the solution and coats the medicaldevice. In polar aprotic solvents such as dimethylformamide (DMF) ordimethylsulfoxide (DMSO), the medical device can be dipped into thereaction mixture and then dried in vacuo or under a stream of an inertgas such as nitrogen or argon, thereby coating the medical device.Suitable nitrosylating agents include acidified nitrite,S-nitrosothiols, organic nitrite, nitrosyl chloride, oxadiazoles,nitroprusside and other metal nitrosyl complexes, peroxynitrites,nitrosonium salts (e.g. nitrosyl hydrogensulfate) and the like. Suitablenitrating agents include organic nitrates, nitronium salts (e.g.nitronium tetrafluoroborate) and the like. The polymers of the presentinvention are not brittle, and consequently remain adhered to themedical device, even under physiological conditions. Thus, thesepolymers are particularly suited for coating devices which are to beimplanted in patients for extended periods of time.

It is to be understood that other methods of applying polymer coatingsto devices, including methods known in the art, can be used to coatmedical devices with the polymers of the present invention.

Another embodiment of the present invention is a method of replacing aloss of NO groups from an S-nitrosylated polymer. As discussed above, NOis lost from S-nitrosylated compounds over time. In addition,sterilization of medical instruments containing S-nitrosylated compoundsalso results in the loss of NO from S-nitrosylated compounds. The lossof NO from S-nitrosylated compounds reduces the capacity of the compoundto deliver NO to a treatment site. NO groups can be replaced bycontacting the S-nitrosylated polymer with an effective amount of agaseous, nitrosylating agent such as nitrosyl chloride or nitric oxide.

An “effective amount” of a gaseous, nitrosylating agent is the quantitywhich results in nitrosylation free thiol groups in the compound orpolymer. Preferably, a sufficient amount of the gaseous, nitrosylatingagent is used to saturate the free thiol groups in the compound orpolymer with NO, i.e. all of the thiol groups become nitrosylated. Aneffective amount ranges from about 0.8 atmospheres to about 10atmospheres and is preferably about one atmosphere.

Another embodiment of the present invention is a method of replacing aloss of NO or NO₂ groups from a nitrated or nitrosylated polymer at atreatment in an individual. The method comprises administering to theindividual a regenerating amount of a nitrating agent or a nitrosylatingagent suitable for regenerations pendant nucleophilic groups with NO₂ orNO groups, as described above. Examples include S-nitrosothiols, organicnitrites, oxadiazoles, metal nitrosyl complexes, organic nitrates,peroxynitrites, nitrosonium salts and nitronium tetrafluoroborate.Although Applicants do not wish to be bound by any particular mechanism,it is believed that some of the nitrating agent or nitrosylating agentwill contact the polymer at the treatment site and nitrate ornitrosylate the free nucleophilic groups in vivo, thereby regeneratingthe NO₂ or NO capacity of the polymer.

A “regenerating amount” of a nitrating or nitrosylating agent is anamount which results in a sufficiently high local concentration of theagent at a treatment site to nitrate or nitrosylate the free pendantnucleophilic groups of a polymer located at the treatment site. A“regenerating amount” is also an amount which does not cause undueundesirable side effects in the individual. It will be understood thatthe amount administered to the individual will depend on factors such asthe age, weight, sex and general health of the individual, and that theskilled person will be able to vary the amount administered, taking suchfactors into account. For example, dosages can be from about 10mg/kg/day to about 1000 mg/kg/day. The compound can be administered byan appropriate route in a single dose or multiple doses.

A variety of routes of administration are possible including, but notnecessarily limited to parenteral (e.g., intravenous, intraarterial,intramuscular, subcutaneous injection), oral (e.g., dietary), nasal,slow releasing microcarriers, or rectal, depending on the disease orcondition to be treated. Oral, parenteral and intravenous administrationare preferred modes of administration. Formulation of the compound to beadministered will vary according to the route of administration selected(e.g., solution, emulsions, aerosols, capsule). An appropriatecomposition comprising the compound to be administered can be preparedin a physiologically acceptable vehicle or carrier. For solutions oremulsions, suitable carriers include, for example, aqueous oralcoholic/aqueous solutions, emulsions or suspensions, including salineand buffered media. Parenteral vehicles can include sodium chloridesolution, Ringer's dextrose, dextrose and sodium chloride, lactatedRinger's or fixed oils. Intravenous vehicles can include variousadditives, preservatives, or fluid, nutrient or electrolyte replenishers(See, generally, Remington's Pharmaceutical Science, 16th Edition, Mack,Ed. (1980)).

The invention is further illustrated by the following examples, whichare not intended to be limiting in any way.

EXEMPLIFICATION Example 1 Preparation ofPer-(6-deoxy-6-iodo)-β-iodocyclodextrin

β-Cyclodextrin (20.0 g, 17.6 mmol, 123 mmol primary hydroxyl) was addedto a stirred solution of triphenylphosphine (97.2 g, 371 mmol, 3 eq perprimary hydroxyl) and iodine chips (93.5 g, 371 mmol, 3 eq per primaryhydroxyl) in dimethylformamide (DMF) (400 mL); the mixture warmed onaddition. The solution was placed in an oil bath at 80° C. for 20 hours,then permitted to cool to room temperature DMF (350 mL) was removedunder reduced pressure to yield a thick, the dark syrup was roughlyone-third the volume of the original solution. To this syrup, cooled inan ice bath, was added 160 mL of 3 M NaOMe; the pH was found to be 9 (pHpaper with a drop of water). After addition, the syrup was permitted towarm to room temperature and stirred for an additional 1 hour. The syrupwas then poured into MeOH (3600 mL) to give a small amount ofprecipitate. Water (1000 mL) was added slowly to the MeOH solution,yielding a milky white precipitate in the dark brown solution. Theprecipitate was removed by filtration to give a yellow solid that waswashed several times with MeOH (1000 mL total) to remove most of thecolor, giving a tan solid that was Soxhlett-extracted for >12 hours anddried under high vacuum to give 19.84 of an off-white solid (59%).

Example 2 Preparation of Per-(6-deoxy-6-thio)β-thiocyclodextrin

Per-(6-deoxy-6-iodo)-β-cyclodextrin (19.84 g, 10.4 mmol, 72.9 mmolprimary iodide) was dissolved in DMF (210 mL) and thiourea (6.3 g, 82.8mmol, 1.13 eq) was added. The solution was stirred at 70° C. undernitrogen for 48 hours. DMF was removed under reduced pressure to give anorange oil, which was added to aqueous NaOH (5.4 g in 1000 mL, 135 mmol)to give a white precipitate on stirring. The solution was heated to agentle reflux for 1 hour, which effected full solvation of theprecipitate, then cooled, which resulted in formation of a precipitatethat was removed by filtration and washed with water (this precipitatewas not used). The solution was acidified with 1 M KHSO₄ to give a finewhite precipitate that was filtered and washed with water, thenair-dried overnight. The precipitate was suspended in water (700 mL),then solvated by addition of 70 mL of aqueous 1 M NaOH, thenre-precipitated with 90 mL of aqueous 1 M KHSO₄. The precipitate wasfiltered, air-dried overnight, then dried under high vacuum to give 6.0g (46%) of an off-white solid, mp 289° C. (dec).

Example 3 Nitrosylation of Per-6-thio-β-cyclodextrin with Acidic Nitrite

Per-(6-deoxy-6-thio)-β-cyclodextrin (500 mg, 0.401 mmol, 2.81 mmolprimary thiol) was dissolved in 0.5 M aqueous NaOH (10 mL) to give afaintly yellow solution. A mixture of 2.8 mL 1 M aqueous NaNO₂ (2.8mmol, 1 equivalent per mole free thiol) and 2 M HCl (15 mL) was quicklyadded to give a brick-red precipitate. The precipitate was pelleted bycentrifuge, and the acidic supernatant was removed by syringe. Deionizedwater was added and the precipitate was agitated to full dispersion. Thecentrifugation/supernatant removal process was repeated six times (untilthe supernatant was neutral to pH paper), giving a deep red pellet in asmall amount of water.

Example 4 Nitrosylation of Per-6-thio-β-cyclodextrin with NitrosylChloride in DMF

Per-(6-deoxy-6-thio)-β-cyclodextrin (50 mg, 0.04 mmol, 0.28 mmol primarythiol) was dissolved in DMF (1 mL). Nitrosyl chloride was bubbledthrough to give a deep brown solution. The solvent can be removed invacuo or under a stream of an inert gas such as nitrogen or argon toafford the polymer product.

Example 5 Nitrosylation of Per-6-thio-β-cyclodextrin withS-Nitroso-N-Acetylpenicillamine

Per-(6-deoxy-6-thio)-β-cyclodextrin (32.3 mg, 0.0259 mmol, 0.181 mmolprimary thiol) was dissolved in 1 mL 1 M NaOH.D(+)-S-nitroso-N-acetylpenicillamine (57.0 mg, 1.4 eq per thiol) wasadded to give a deep-red precipitate. The precipitate was pelleted bycentrifuge, and the acidic supernatant was removed by syringe. Deionizedwater was added and the precipitate was agitated to full dispersion. Thecentrifugation/supernatant removal process was repeated four times(until the supernatant was neutral to pH paper), giving a deep redpellet in a small amount of water.

Example 6 Nitrosylation of Per-6-thio-β-cyclodextrin withS-Nitroso-N-Acetylpenicillamine in Dimethylformamide

Per-(6-deoxy-6-thio)-β-cyclodextrin (10 mg, 0.0080 mmol, 0.056 mmolprimary thiol) was dissolved in 1 mL DMF.D(+)-S-nitroso-N-acetylpenicillamine (17.7 mg, 0.080 mmol, 1.4 eq perthiol) was added to give a green solution. After standing for 2 hours,the solution had turned deep red. The solvent can be removed in vacuo orunder a stream of an inert gas such as nitrogen or argon to afford thepolymer product.

Example 7 Method for Assaying Nitric Oxide Release

The capacity of a compound to cause relaxation of vascular smoothmuscle, measured by the degree and duration of vasodilation resultingfrom exposure of a blood vessel to the compound, is a measure of itsability to deliver NO in vivo. Methods reported in Stamler et al., Proc.Natl. Acad. Sci. USA 89:444 (1992), Osborne et al., J. Clin. Invest.83:465 (1989) and the chapter by Furchgott in Methods in Nitric OxideResearch, edited by Feelisch and Stamler, (John Wiley & Sons) (1996),were used to measure vascular smooth muscle contraction. Because lowerconcentrations of NO are required to inhibit platelet aggregation thanvasodilation, measurement of smooth muscle contraction provides a goodindication of whether a composition delivers sufficient NO to reduceplatelet aggregation.

New Zealand White female rabbits weighing 3-4 kg were anesthetized withsodium pentobarbital (30 mg/kg). Descending thoracic aorta wereisolated, the vessels were cleaned of adherent tissue, and theendothelium was removed by gentle rubbing with a cotton-tippedapplicator inserted into the lumen. The vessels were cut into 5-mm ringsand mounted on stirrups in 20 mL organ baths. The rings were suspendedunder a resting force of 1 g in 7 ml of oxygenated Kreb's buffer (pH7.5) at 37° C. and allowed to equilibrate for one hour. Isometriccontractions were measured on a Model 7 oscillograph recorder connectedto transducers (model TO3C, Grass Instruments, Quincy, Mass.). FreshKrebs solution was added to the bath periodically during theequilibration period and after each test response. Sustainedcontractions were induced with 7 μM norepinephrine prior to the additionof the test compound.

Example 8 Delivery of Nitric Oxide by a Polymer Coated Stent

The ability of S-nitrosylated β-cyclodextrin (referred to as “freepolymer”) to cause continuous vasodilation was compared with theNO-related activity of a stent coated with S-nitrosylatedβ-cyclodextrin. S-nitrosylated β-cyclodextrin was obtained by the methoddescribed in Example 3. Polymer-coated stents were obtained bysuspending a stent in the reaction mixture prepared according to theprocedure described in Example 3, thereby allowing the precipitatedS-nitrosylated β-cyclodextrin to coat the stent. Alternatively,polymer-coated stents were obtained by dipping a stent into a reactionmixture prepared by the method of Example 4. In either case, thepolymer-coated stent was then dried in vacuo or under a stream of anitrogen. The delivery of NO by the polymer coated stent and by the freepolymer was assayed according to the procedure described in Example 7.

The polymer coated stent resulted in continuous vasodilation for morethan one hour. Removal of the stent resulted in immediate restoration oftone, indicative of continuous NO release.

A fresh polymer coated stent was added to the organ chamber. The stentwas then removed from the organ chamber and transferred to a secondorgan chamber. Similar levels of smooth muscle relaxation were observedto occur in each organ chamber, which is indicative of continuousrelease of NO from the S-nitrosylated β-cyclodextrin.

Example 9 Stability of Polymers Prepared by NitrosylatingPer-6-Thio-βCyclodextrin with S-Nitroso-N-Acetylpenicillamine

The S-nitrosylated polymer prepared by the method described in Example 5was placed on a metal base and dried in vacuo or under a stream ofnitrogen to give a brown solid. This solid had an absorabance of about15 in the visible range from about 540 to about 600 nanometers.Concentrations of NO in the 1.0 mM range are sufficient to give anabsorbance of about 0.15 in this region of the visible spectrum.

The polymer was then stored and protected from light for three weeks.The absorbance in the region from about 540-600 nanometers wasessentially unchanged, indicating retention of S—NO by the polymer. Inaddition, the ability of the compound to cause vasodilation, as measuredby the assay described in Example 7, also remained essentially unchangedover the three week period.

Example 10 Incorporating S-Nitroso-N-Acetylpenicillamine IntoS-Nitrosylated Polymers Increases the Nitric Oxide Delivering Capacityand Half-Life of the Polymers

S-Nitroso-penicillamine, S-nitrosylated β-cyclodextrin (preparedaccording to the procedure in Example 3) and S-nitrosylatedβ-cyclodextrin complexed with S-nitroso-penicillamine (preparedaccording to the procedure in Example 5) were assayed by the methoddescribed in Example 7 for their ability to cause vasodilation. Inaddition, the half-lives for these compositions in physiologicalsolution were measured. The half-life is time required for thecomposition to lose one half of its bound NO. The amount of NO in thecomposition is determined by the method of Saville, as described inExample 13.

S-nitrosylated β-cyclodextrin complexed with S-nitroso-penicillamine wasfound to deliver several orders of magnitude more NO in physiologicalsolution than S-nitroso-penicillamine. In addition,S-nitroso-penicillamine was able to deliver NO for no more than aboutone hour, while S-nitrosylated β-cyclodextrin complexed withS-nitroso-penicillamine had a half-life of greater than forty hours.This result indicates that incorporating S-nitroso-penicillamine intothe polymer matrix results in stabilization of theS-nitroso-penicillamine —S—NO group.

Incorporation of S-nitroso-penicillamine into the polymer matrix ofS-nitrosylated β-cyclodextrin resulted in an extension of the timeperiod during which nitric oxide can released. The half-life ofS-nitrosylated β-cyclodextrin was greater than about eighteen hours,while the half-life of S-nitrosylated β-cyclodextrin complexed withS-nitroso-penicillamine was greater than about forty hours. This resultindicates that it is possible to extend the time period during whichS-nitrosylated polymers can release NO, based on the type of NO donorthat is incorporated into the polymer matrix. This result also suggeststhat the NO donor is “empowering” the polymer with NO activity, thusserving to extend the polymer lifetime.

Example 11 Assay For Determining Antiplatelet Effects

Venous blood, anticoagulated with 3.4 mM sodium citrate was obtainedfrom volunteers who had not consumed acetylsalicylic acid or any otherplatelet-active agent for at least 10 days. Platelet-rich plasma wasprepared by centrifugation at 150×g for 10 minutes at 25° C. Plateletcounts were determined with a Coulter Counter (model ZM).

Aggregation of platelet-rich plasma was monitored by a standardnephelometric technique, in which 0.3-ml aliquots of platelets wereincubated at 37° C. and stirred at 1000 rpm in a PAP-4 aggregometer(Biodata, Hatsboro, Pa.).

S-Nitrosylated β-cyclodextrin, prepared according to the methoddescribed in Example 3, was incubated at concentrations of 1 μM, 10 μMand 100 μM in 400 μL of platelet rich plasma for 3 minutes. Aggregationswere induced by adding 100 μL of 10 μM ADP. Controls were run in theabsence of polymer. Aggregations were quantified by measuring themaximal rate and extent of change of light transmittance and areexpressed as normalized value relative to control aggregations.

Dose-dependent inhibition of ADP-induced platelet aggregation wasobserved over the range of 1 μM to 100 μM S-nitrosylated β-cyclodextrin.Inhibition of platelet aggregation was observed, even at the lowestconcentration.

Example 12 Inhibition of Platelet Deposition in Dogs by S-Nitrosylatedβ-Cyclodextrin Coated Stent

Platelets play a central role in the development of acute closure aswell as late restenosis following angioplasty. Potent inhibitors of theplatelet glycoprotein II_(B)/III_(A) when given systemically have beenshown to be effective in reducing 30 day and 6 month clinical eventsfollowing high risk angioplasty. This benefit, however, has come at theexpense of higher rates of bleeding complications. By delivery of apotent glycoprotein II_(B)/III_(A) inhibitor locally, the benefits ofplatelet inhibition may be attained without the risk of systemicplatelet inhibition. The purpose of this study is to determine the localplatelet inhibitory effects of cyclodextrin-nitric oxide.

Methods

Seven mongrel dogs were studied. After diagnostic angiography, stentswere implanted into the LAD and LCX arteries. The first 3 animalsreceived plain 8 mm corrugated metal ring stents and the remaining 4were given SNO-cyclodextrin coated stents. Coronary dimensions wereobtained utilizing on-line QCA measurements and stents wereappropriately sized to achieve a 1.2-13:1 stent to artery ratio. Priorto stent implantation, autologous platelets were labeled with Indium 111oxime, reinfused and allowed to recirculate for 1 hour. The assignedstents were then deployed at 10-14 ATMs and quantitative coronaryangiography was repeated. Platelets were allowed to circulate anadditional 24 hours then the study was terminated for plateletdeposition analysis.

Results

Platelet deposition on plain metal stents was greater than on NO coatedstents although the difference was not statistically significant:5.19±5.78 vs. 4.03±5.33 platelets×10⁸/cm² p=0.5827. However, 4 of the 6metal controls had greater platelet deposition than any of the NO coatedstents. The mean for the metal controls was affected by 2 very lowvalues. These data suggest that the drug prevents above baselineplatelet deposition as was seen in 4 of the 6 metal stents without NOcoating. The number of platelets/square centimeter on each of thecontrol stents and on each of the coated stents are shown in FIG. 1.

Example 13 Determination of the Amount of S-Nitrosylation inS-Nitrosylated Polysaccharides

Determination of Carbohydrate Concentration

The amount of carbohydrate present is determined by the followingdisclosed in Dubois et al., Anal. Chem. 28:350 (1956). Two millilitersof carbohydrate solution containing between 10 and 70γ of carbohydrateare pipetted into a colorimetric tube, and 0.05 ml of 80% phenol isadded. Then 5 ml of concentrated sulfuric acid is added rapidly, thestream of acid being directed against the liquid surface rather thanagainst the side of the test tube in order to obtain good mixing. Thetubes are allowed to stand 10 minutes, then they are shaken and placedfor 10 to 20 minutes in a water bath at 25° C. to 30° C. before readingsare taken. The color is stable for several hours and readings may bemade later if necessary. The absorbance of the characteristicyellow-orange color is measured at 490 mμ of hexoses and 480 mμ forpentose and uronic acids. Blanks are prepared by substituting distilledwater for sugar solution. The amount of sugar may then be determined byreference to a standard curve previously constructed for the particularsugar under examination.

All solutions are prepared in triplicate to minimize errors resultingfrom accidential contamination with cellulose lint.

Determination of R—S—NO Concentration

The concentration of R—S—NO groups in a sample is based on the methodreported in Saville, Analyst 83:620 (1958). By this method, R—S—NOgroups are converted into an azo dye. The concentration of this dye isdetermined by measuring the absorbance at 540 nm (ε˜50,000 M⁻¹ cm⁻¹).The procedure is as follows:

Reagents

-   Solution A: sulfanilamide 1% dissolved in 0.5 M HCl.-   Solution B: same solution as used in A to which 0.2% HgCl₂-   Solution C: 0.02% solution of N-(1-naphthyl)-ethylenediamine    dihydrochloride dissolved in 0.5 M HCl.    Procedure

A given volume (50 μl-1 m) of the sample to be assayed is added to anequivalent volume of solution A and solution B. The two samples are setaside for 5 minutes to allow formation of the diazonium salt, afterwhich an equivalent volume of solution C is added to each mixture. Colorformation, indicative of the azo dye product, is usually complete by 5minutes. The sample absorbance is then read spectrophotometrically at540 nm. The RSNO is quantified as the difference in absorbance betweensolution B and A. (i.e. B−A). In the event that the background nitriteconcentration is high (i.e. increased background in A), the accuracy ofthe measurement can be increased by the addition of an equivalent volumeof 0.5% ammonium sulfamate in acid (45 mM) 5 minutes prior to theaddition of sulfanilamide. The nitrous acid in solution reactsimmediately with excess ammonium sulfamate to form nitrogen gas andsulfate.

Concentrations of thiol greater than 500 μM in samples may interferewith the assay if nitrite is also present at micromolar concentration.Because nitrite will nitrosate indiscriminantly under the acidicconditions employed, thiols will effectively compete for reaction withsulfanilamide (present at 50 mM in this assay) as their concentrationapproaches the millimolar range. This will lead to artifactual detectionof RSNO. The problem can be avoided by (1) keeping the ratio of thiol tosulfanilamide<0.01, (2) first alkylating thiols in the solution, or (3)adding free thiols to standards to correct for the potential artifact.

S-nitrosylated β-cyclodextrin was prepared as described in Example 3using 1 mM perthiolated β-cyclodextrin and 1) one equivalent (1×); 2)two equivalents (2×); three equivalents (3×); six equivalents (6×); andten equivalents (10×) of acidic nitrite. The carbohydrate concentrationand the —S—NO concentration of each resulting carbohydrate polymer wasthen determined, as described above. The results are shown in FIG. 2. Asix fold excess of acidified nitrite results in about three —S—NO groupsper molecule of cyclodextrin, or about one —S—NO group per 470 molecularweight. The use of three and ten equivalents of acidified nitriteresults in a product with between about 2 and 2.5 —S—NO groups percyclodextrin.

Example 14 Preparation of O- and S-Nitrosylated β-Cyclodextrin

β-Cyclodextrin with pendant —O—NO and —S—NO groups was preparedaccording to the procedure described in Example 3 except that 50 and 100equivalents of acidic nitrite were used.

The formation of —O—NO groups is accompanied by an increase inabsorbance in the 320-360 nm range of the ultraviolet/visible spectrum.Because —S—NO groups also absorb in this region of theultraviolet/visible spectrum, confirmation of O-nitrosylation isprovided by the observation that the increase in absorbance in the320-360 nm region is accompanied by no further increase in the —S—NOconcentration. The concentration of —S—NO is determined by the method ofSaville, described in Example 13. The amount of —O—NO present in thepolymer can be determined by the intensity of the absorbance in the320-360 nm region and the loss of NO from media. The quantity of —O—NOper molecular weight can be calculated by first determining thecarbohydrate concentration, as described in Example 13 above.

FIG. 3 shows the ultraviolet/visible spectrum of the β-cyclodextrin inthe presence of a 50 fold excess of acidic nitrite, as described above.As can be seen, the absorbance in the 340-350 nm region increases overtime, with a maximum being reached after about 45 minutes. The combinedconcentration of —O—NO and —S—NO groups was determined to be about 10 NOgroups per cyclodextrin when a 50 fold excess of acidic nitrite wereused or about one NO group per 140 amu. The combined concentration of—O—NO and —S—NO groups was determined to be about 21 NO groups percyclodextrin when a 100 fold excess of acidified nitrite were used orabout one NO group per 67 amu.

Example 15 General Procedure for the Preparation of Polymers WithStabilized S-Nitrosylated Groups

All precursor thiols were obtained from Sigma-Aldrich Chemical Co. andwere used without further purification. Tertiary-butyl nitrite (TBN,96%) was purchased from Aldrich Chemical Co. and was used withoutfurther purification.

Polythiol and TBN were mixed neat and allowed to stir at roomtemperature. 0.5 equivalents of TBN were used for each equivalent offree thiol present in the polythiol. The reaction vessel was then sealedto exclude oxygen and wrapped in aluminum foil to exclude light.

The following polythiols were reacted with TBN according to theprocedure described in the previous paragraph:

Polythiol 1-Trimethylolpropane Tris(3-Mercaptopropionate)

Polythiol 2-Pentaerythritol Tetrakis-(3-Mercaptopropionate)

Polythiol 3-1,2,6-Hexanetriol Trithioglycolate

Polythiol 4-Trimethylolpropane Tris(2-Mercaptoacetate)

In each case, the reaction mixture rapidly turned a deep red aftermixing the polythiol and TBN. The red color is indicative ofS-nitrosylation. After standing for about two weeks, each reactionmixture appeared as a pink-gel like solid. The color persisted in eachcase for at least three weeks, indicating that the polymers retained theability to release NO was retained during this period of time. As shownin Example 16, polymers that were one week old released sufficient NO torelax vascular smooth muscle.

Example 16 Relaxation of Vascular Smooth Muscle by the Polymers WithStabilized S-nitrosyl Groups

The capacity of the polymers prepared in Example 15 to relax vascularsmooth muscle was determined by the method described in Example 7,modified to use descending thoracic aorta obtained from Wistar rats.20.5 mg of Polythiol 1, 7.1 mg of Polythiol 2, 25.5 mg of Polythiol 3and 6.6 mg of Polythiol 4 were tested independently. All polymers hadbeen prepared at least one week prior to testing. In each case,relaxation of the smooth muscle occurred within one minute of adding thetest polymer.

Equivalents

Those skilled in the art will know, or be able to ascertain using nomore than routine experimentation, many equivalents to the specificembodiments of the invention described herein. These and all otherequivalents are intended to be encompassed by the following claims.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A polymer derivatized with at least one —ONO group per 1200 atomicmass units of the polymer.
 2. The polymer of claim 1 comprising at leastone —ONO group per 600 atomic mass units of the polymer.
 3. An articlecapable of releasing NO wherein the article is coated with a polymercomprising at least one —ONO group per 1200 amu of the polymer.
 4. Thearticle of claim 3 wherein the article is a medical device forimplantation in a subject or a tube or catheter for contacting thebodily fluid of a subject.
 5. A method of delivering nitric oxide to atreatment site in a subject or to a bodily fluid comprising the stepsof: a) providing a medical device coated with a polymer having at leastone —ONO group per 1200 amu of the polymer; and b) implanting themedical device at the treatment site or contacting the bodily fluid withthe medical device.
 6. A method of preparing an article capable ofreleasing NO comprising coating an article with at least one —ONO groupper 1200 amu of the polymer.
 7. The method of claim 6 wherein thearticle is a medical device for delivering nitric oxide to a treatmentsite in a subject or a tube or catheter for contacting a bodily fluid ofa subject.
 8. The polymer of claim 1 wherein the polymer isnon-peptidyl.
 9. The polymer of claim 2 wherein the polymer isnon-peptidyl.
 10. The polymer of claim 1, wherein the polymer isprepared from a polymer having a multiplicity of hydroxyl groups. 11.The polymer of claim 5 wherein the polymer can form a hydrogel.
 12. Amethod of replacing a loss of NO groups from an O-nitrosylated polymerat a treatment in an individual, said method comprising the step ofadministering to the individual a regenerating effective amount of anitrosylating agent.